Relation between neutral hydrogen mass and luminosity for spiral and irregular galaxie

Huang, S.-S.

English

NASA Technical Reports Server

- - - - -  Os T i i  ~IBSC3-L3XI:~OSIIY R E L A T I O X  F ' O 3  S? ILkL  G=-LLLLZJ 
Su-Shu Huang 
Dearbcrn Observatory, Northwestern Univers i ty  
Received I 
Revised 
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UCCESSION N MBER)  - i  f - '\\ 
I- - (P GE5)  
j c/-7r3rq 
(NASA C R  O R  TUX O R  AD NUMBER) 
ABS TRpCr 
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The mass-1u.nfnosity r e l a t i o n  f o r  s p i r a l  and i r r e g u l a r  
/f@/ c UT2 
g a l s x i e s  f o u 6  by Pskovski i  and a s i m i l a r  r e l a t i o n  betweenAfF ' ~ 5% 
the mass of n e u t r a l  hydrogen and the luminosity noted  h e ~ e  
l e a d  t o  a r e l s - t i on  between t h e  total mass and the  mass of 
n e u t r a l  hydrogen for t h e s e  ga l ax ie s .  SeveTal hypotheses 
have been advsliced i n  order  t o  understand t h i s  r e l a t i o n .  
Poveda (1961) discovered tha t  t h e  dust-?oor s t e l l a r  
systems obey E mass-luminosity r e l a t i o n ,  which has f u r t h e r  
been conf i -nee  by Pskovskii  (1965). If we denote by arrd 
.G 
r e s 2 e c t i v e l y  the  mass and the  phofsgrazkis l x m i r i o s i t g  0; 
of a galaxy, -their r e l a t i o n s  can be written as 
https://ntrs.nasa.gov/search.jsp?R=19660028272 2020-03-16T17:31:38+00:00Z
e 
was derived frm e n p i r i c a l  r e s u l t s  of 13 galax ies  whose 
t o t a l  masses, x ,  have been determined d i r e c t l y  p lus  
another  13  ga lax ie s  of which only t h e  masses 
n e u t r a l  hydrogen a r e  known through t h e  observa t ions  o f  t h e  
21 cm. l i n e .  Since both t h e  t o t a l  masses and t h e  masses of 
t h e  n e u t r a l  hydrogen i n  t h e  f i r s t  13 g a l a x i e s  have been de tez-  
mined, Pskovskii  has reduced from them an empir ica l  r e l a t i o n  
and the photograpnic magnitude between the r a t i o  tf /zc 
of t h e  galaxy. From this r e l a t i o n ,  he i s  a b l e  t o  d e r i v e  
M f l  
the t o t a l  m a s s  of each galaxy from t h e  mass of i t s  ne i l t ra l  
hydrogen f o r  the  second 13 galaxies.  
Pskovski i?  s procedure is l e g i t i m a t e ,  and his  m-z 
r e l a t i o n  f o r  s p i r a l  and i r r e g u l a r  ga l ax ie s  i n t e r e s t i n g ,  b u t  
w e  would l i k e  t o  t ake  a d i f f e r e n t  look a t  the  problein. While 
the luminosity of a dust-poor s t e l l a r  system i s  perhaps con- 
t r l b u t e d  by t k e  r e d  g i a n t  s t a r s  and s ta rs  on t h e  h o r i z o n t a l  
branch i n  t h e  5-3 diagram, the  dominant s o w c e  of luminosity 
In b. s p l r a l  or- an i r r e g u l a r  galaxy c o n s i s t s  *without doubt of 
the early-t3Tr. and suTer-giant s t a r s  that  a r e  r e l a t i v e l y  g o n g ; .  
In o t h e r  words, t h e  luminosity of t h e  s p l r a l  s y s t e n  comes 
mainly from tke stars that are r e c e n t l y  forrried oilt oT t he  
gaseous mediur.. If so, one would expect  a r e l a t i o n  between 
the IQSSS of n c u t r a l  hydrogen flH ( i n s t e a d  of t h e  total z & s s  
I 
1 ar,d thz l u n i n o s i t y  f o r  :hzse galaxies. ~o1101zring 
t'nls reasonin;, we have ? l o t t e d  i n  Figure 1 t h e  r e l a t i o r ,  
- I  I* 3 e  t%'e $FA Lzc trAc ?hoTo;ra?hic sb3;:*Azs .x-;*:~~: - 
d -. 
L/ 
.. 3 
- 2 -  
L 
f o r  26 galaxi~s f i s t e d  i n  Pskovski i ' s  paper. 
s o l u t i o n  & i c k  w a s  obtained on t h e  7094 computer by Mr. Chrsr.;e 
blade, Jr. a t  Goddard Space F l i g h t  Center, from t h e  e n p i r i c a l  
p o i n t s  i n  t h e  f i g u r e  gives  
'The ledst-s<,sre  
which i s  represented  by the straight l i n e  i n  t h e  f i g u r e .  
corresponds t o  r e l a t i o n  (1) w i t h  & =  1.43. 
solved i n  t e r m  of l o g  b;reH 
o b t a i n  a= 1.19. Whichever d. value  we t ake ,  t h e  r e l a t i o n  
thus found i s  now easy t o  i n t e r p r e t  because t h e  niore n e u t r a l  
hydrogen a s p l r a l  o r  an i r r e g u l a r  galaxy conta ins ,  the  more 
b r i g h t  young s tars  w i l l  be formed which inc rease  t h e  fuminos iQ 
of t h e  e n t i r e  galaxy. 
Actual ly  t h e  t o t a l  luminosity 2 of a s p i r a l  o r  ax i r r e g -  
It 
If % is 
i n  t h e  l ea s t - squa re  s o l u t i o n ,  we 
ular  galaxy i s  composed of two sources: 
young stars j u s t  emerging from gaseous media we have d i scussed ,  
(1) 2 due to the 
d 
and ( 2 )  2e/, due t o  t h e  older stars (main-sequence stars of 
s p e c t r a l  type A and l a t e r ,  and populat ion I1 giant s ta rs ) .  
1umir.oslty a r i s i n g  f r o m  the f i r s t  s o u r c e  i s  a f u n c t i o n  of' zr 
x h i l e  t he  lxn inos i ty  a r i s i n g  from t h e  second source  has a de- 
sendence on &r If t h e  photographic luniinosity of t h e  s~ 
kir6s of gr1e:;ie:j.s indeed der ived  mainly from the f i r s t  source,  
t h e  r e s u l t  o f  CC = 1.43 i n  p r o 2 o r t i o c a i i t y  {i) iniI!ic:&Zes t h a t  
Tkc: 
tl 
H *  
- 3 -  
T h i s  snows i n  t u r n  that the  r a t e  of f o m i t i m  or' 8 ta r s  a l so  
inc reases  fas l ;er  than the  gaseous m a t t e r  aval lable .  
Presumably & m a y  b e  r e l a t e d  t o  tine mode of star f o x a -  
t i o n  i n  t h e  i n t e r s t e l l a r  clouds. If s tars  are formed fns i ie  
the cloud, & may be near ly  equal t o  one. If, on the o t h e r  
hand, formation should be favcrabie  a t  t h e  boundary of t w o  
c o l l i d i n g  clocds,  perhaps & would be equal t o  two. Being 
between one ar,d two t h e  determined & value seems reasonable.  
The f a c t  that both  m-$, and 3cdpH -% r e l a t i o n s  
exist only shows t h a t  T& and ah are cor re l a t ed .  From 
the t h i r t e e n  s p i r a l  g a l a x i e s  whose a and are known, 
we have found by t h e  l e a s t  square s o l u t i o n  t h a t  
kf 
of e i f f e r e n t  :.,asses. 
f o r  t h e  ex i s t ence  of t h i s  r e l a t i o n :  
We may o f f e r  t h r a e  t e n t a t i v e  h jTotkeses  
(1) A chance coincidence. For each galaxy zch a t  any 
t h e  n u s t  depend i n  genera l  upon t h e  total y.ass and i t s  age. 
It is a two-vAriable f i n c t i o n .  mat i s  only a function 
11 
e+- -n-P -LA--- A L  - L  IrilL J L ~ U H Y  L L I U L ,  It is a coinc idenca  if r;he g a a l a i e s  were 
- 4 -  
fo; d i f f e r e n t  systems. 
i s  very s m a l l .  
The chame of this coincidence ,?er'r-,a?s 
, 
I 
(2) Formation of stars in t h e  galaxy t ak ing  p l ace  mainly 
in t h e  early stage.  
result of t h e  i n i t i a l  batch of star formation. In the l a t e r  
s t a g e s  the gas shed by evolving stars may roughly balance its 
dep le t ion  through s t a r  formation. In o t h e r  words, i n  
each galaxy is roughly i n  a state o f  equi l ibr ium and t h e  
r e l a t i o n  w i l l  be only slightly modif'ied as time goes on. Con- 
sequent ly  ever, though the ga lax ie s  may be f orxed a t  d i f f e r e n t  
t imes,  the saxe n-x~ r e l a t i o n  w i l l  p e r s i s t  a t  any time. 
Also the xH-z r e l a t i m  w i l l  n o t  change GreatZy w i t h  t i n e .  
( 3 )  Stars forming gradually i n  each galaxy but  a11 galax- 
If so, the a-&f~ r e l a t i o n  was t h e  
H 
- JcH 
ies forned a t  about t he  sm-e time. I n  such a c a s e  t h e r e  will 
be a m-zCfl r e l a t i o n  at any given time but  t h e  form of this 
r e l a t i o n  changes w i t h  time. Whether the -L r e l a t i o n  
will remain the sane depends upon the nanner i n  which t h e  r a t e  
of star formatioT1 varies with t he  decreasing xh .
O f f  
If e i t h e r  nypothesfs ( 2 )  o r  ( 3 )  tcms out to be c o r r e c t ,  
it appears that s tar  formation i n  the  spiral o r  i r r e g u l a r  
galaxies a t  ar~y time depends dominant ly  on ly  upon ?+ ",LY &Td 
perhaps also :x . 
of galaxies accopding t o  t h e  standard c l a s s i f i c a t i o n  must 
~1esc l t  f m x  SGZS ~ a ~ a - ~ ~ e t e r s ,  such as  t h e  mzu la r  z i o n e a t w  per  
u n i t  m a s s ,  e tc . ,  which do not play a de te rx in ing  e f f e c t  oil s t a ~  
I t  foll.ows t h a t  t h e  rnor2holosical seq;ie:rrca 
fox:ilJCIon. T r  tve xat; E ~ S O  co;-iclude that t h e  s 2 f r s i  (0:- i T : - C < L Z y  
- 5 -  
galaxy and t l 2  e l l i p t i c a l  galaxy a r e  r,ot g e n e t i c a l l y  r e ~ a c e d ,  
namely they  do not  form an evolut ionary sequence, because 
none of %ha s 2 i r a l  ( o r  i r r e g u l a r )  g a l a x i e s  i n  the mass rayge 
considered has exhausted i t s  n e u t r a l  hydrogen w h i l e  many 
e l l i p t i c a l  g a l a x i e s  e x i s t  i n  t h a t  same mass range. 
/a decreases  w i t h  . T h i s  would pLe r a t i o  MQ 
)t 
show t k a t  t h e  proport ion of xh w i t h  r e spec t  t o  the t o t a l  
mass decreases  more r a p i d l y  w i t h  t i n e  i n  more massive galax- 
i es  thm less massive ones. 
w i t h  O( 2 j 
Such a suggest ion i s  c o n s i s t e n t  
in t'ne mH -z r e l a t i o n  obtained previously.  
Both hypotheses ( 2 )  and ( 3 )  r ep resen t  i d e a l i z e d  cases.  
Actually, perhaps t h e r e  i s  a high r a t e  of star formation i% 
the beginning which determices t h e  i n i t i a l  m-d?f 
t i o n .  But i n  the  l a t e  s tages  s ta r  fo rxa t ion  cont inuous ly*  
d e p l e t e s  nhl a t  an  appreciable  r a t e .  
rela- H 
Consequently t h e  
r s l a t i o n  i s  s i g n i f i c a n t l y ,  though perhaps not .  m-mh 
d r a s t i c a l l y ,  xodi f ied .  If the g a l a x i e s  were formed a t  d i f f e r -  
en t  tixes, thLs would produce a s c a t t e r  of p o i n t s  f ro r i  t h e  
XL- &)f" r e l a t i o n .  
F i n a l l y  i t  i s  a p l easu re  t o  acknowledge my sincere thank5 
to D r s .  E. N .  L h b e r ,  D. E. Osterbrock, m d  A. Poveda f o r  
va luab le  d iscxss ions  and corniunications, aqd t o  Xr. Cla rmce  
Wade, ;re f o r  ob ta in ing  t h e  least-squ&?e so17cltlons on the 
IEC; cox2uter a t  Goddard Space F l i g h t  C e n t e r .  A p & r t  of t h i s  
investization 2s  supported by National.  Aeronautics and S2cce  
~ u ~ Z n i . ~ - t ~ & . t l ~ - ;  -xLiey a r e s e m c h  g r a n t .  , -  
. 
b 
REFEREXCES 
~ 
~ 
Morgan, W. W. 1959, Pub. A. S. P. 71, 92. 
Poveda, A. 1561, Ap. J., u, 910. 
Pskovskii, J. P. 1965, Soviet  Astronony ( A J ) ,  9, 253. 
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a 
0 
Legend 
Fig. 1 - An e r q i r i c a l  r e l a t i o n  between the  mass of neutral 
hydrogen NH and the photographic absolute magnitude 
for sp ira l  galaxies.  
( 2 )  i n  the text was der ived  from the 26 empir ical  points 
shown i n  the f igu re .  
The s o l i d  l i n e  t h a t  r ep resea t s  equation 
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On the mass-luminosity relation for galaxies

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